: We compile the most recently measured and calculated cross sections for processes relevant to annihilation of positrons in solar flares and present the final evaluated cross sections. We calculate the 511 keV annihilation line spectrum and relative strength of the 3gamma continuum for each of the annihilation processes, using a Monte Carlo code that simulates the thermalization of and positronium production by MeV positrons. We calculate the thermally-averaged annihilation and positronium production rates and the positronium quenching rates. We apply the results to four specific environments (fully ionized, neutral, partially ionized and a non-LTE model of the quiet solar atmosphere), calculating the relative strengths of each process and the combined total annihilation line spectrum. The results are compared with data obtained recently from the high spectral-resolution detectors of RHESSI. We find that positron annihilation in solar flares can occur in a wide variety of environments. The cross sections presented here are also useful for evaluation of positron annihilation in other environments such as the interstellar medium.

The Physics of Positron Annihilation in the Solar Atmosphere

Dynamics of positronium (Ps) formation in an arbitrary s-state from an arbitrary s-state of the hydrogen atom in weakly coupled plasma has been investigated within the framework of a distorted-wave theory. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. Using simple variational hydrogenic wave functions and arbitrary order derivatives of the general three-denominator Lewis integral partial-wave scattering amplitudes have been obtained in closed forms. These distorted-wave scattering amplitudes have been used to make a detailed study on differential and total cross sections. It has been found that screening of the interaction potentials has significant effect on the scattering dynamics. Some notable features of cross sections have also been revealed.

Dynamics of positronium formation in positron-hydrogen collisions embedded in weakly coupled plasmas

The scattering amplitude for positron-hydrogen collisions has been conveniently derived within the framework of distorted-wave theory by approximating the distortion potential in a particular channel as the average of perturbation of that particular channel over the bound states. A real advantage of this method is that a few straightforward calculations yield the expression of scattering amplitude as a function of partial wave. The method has been successfully applied to study 1s-2s excitation of hydrogen atom by positron impact and Ps(ns) (n=1,2,3) formation in positron-hydrogen collisions in the intermediate and high energy range. Further to bring the scattering amplitudes in tracktable forms we have formulated an effective and efficient method for evaluating general three-denominator Lewis integral. The results compare nicely with other theoretical and experimental results available in the literature.

Distorted-wave theory for positron-hydrogen collisions

This paper compares the best distorted-wave model results with the most recent experimental data in positron ionization of atomic hydrogen and noble gases. The re-calibration of the experimental measurements yields good agreement with our DCPE5 model at high energies for all the target atoms studied.

Distorted-wave models in positron impact ionization of atoms

We have applied the hidden-crossing method to compute {ital S}-, {ital P}-, and {ital D}-wave cross sections for Ps formation in positron-hydrogen collisions in the Ore gap. The hidden-crossing method has provided a physical explanation of why the {ital S}-wave cross section is so small and why the {ital D} wave is significant. The one-Sturmian theory is used to correct the hidden-crossing theory to take into account the factor ({l_angle}{var_phi}{vert_bar}d{sup 2}{var_phi}/dR{sup 2}{r_angle}+(1/4)/R{sup 2}). We have considered this correction term in computing the {ital P}- and {ital D}-wave cross sections. The hidden-crossing results are compared with accurate results from other methods. This comparison helps assess the accuracy of the hidden-crossing method in describing three-body collisions. {copyright} {ital 1999} {ital The American Physical Society}

Application of the hidden-crossing method to positronium formation

Positronium formation (Ps) cross sections for positrons impinging on atomic hydrogen were measured in the impact energy range from 13 to 255 eV at the High Intensity Positron (HIP) beam at Brookhaven National Laboratory (BNL). The Ps-formation cross section was found to rise rapidly from the threshold at 6.8 eV to a maximum value of (2.98±0.18) ×10−16 cm2 for ∼15 eV positrons. By 75 eV it drops below the detection limit of 0.17×10−16 cm2 which is the present level of statistical uncertainty. A more elaborate data analysis was performed leading to somewhat smaller cross sections than originally published [1]. During the course of this experiment further relative data on impact-ionization cross sections were accumulated.

Results of the Bielefeld-Brookhaven e+-H experiment

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

W. Raith

Author Tools

Chat about Author

Papers

Results of the Bielefeld-Brookhaven e+-H experiment